Tube drawing process



Nov. 22, 1932. H. VON FORSTER YTUBE DRAWING PROCESS 4 SheetsSheet l inFiled May 13, 1950 w- W W E! I: I: i w 1' I I ll I 1 I l F'l I l l II II: i 1 1' I! H H I "1' i I l "N l l I I 1' 1* l I l l i I In venfpn:

Nov. 22, 1932. H. VON FORSTER TUBE DRAWING PROCESS Filed May 13. 1930 4Sheets-Sheet 2 ill ulli'lnunllnm lll ihlllllllllz NOV. 22, VQN FORSTERTUBE DRAWING PROCESS Filed May 13, 1950 4 Sheets-Sheet 3 /n venfor': W W

1932 H. VON FORSTER TUBE DRAWING PROCESS 4 Sheets-Sheet 4 Filed May 13.1950 Patented Nov.. 22. 1932 UNITED STATES PATENT OFFICE HERMANN VONFORS'IEB, OF NIEDERURSEL, NEAR FRANKFORT-ON-THE-MMN, GER- MANY, ASSIGNOR'10 AMERICAN LURGI CORPORATION, OF NEW YORK, N. Y., A COB- IPORATION OFNEW YORK TUBE DRAWING PROCESS Application filed May 13, 1930, Serial No.452,093, and in Germany December 21, 1927.

stages during the operation.

In drawing hollow bodies over a mandrel according to the presentinvention, the hollow body is loosened from the mandrel, after eachdraw, or after a small number of draws, in order to be further drawn onthe same mandrel. Several loosening and drawing operations can beperformed in succession on the same mandrel.

The invention prevents the risk of tension cracks due to the tubeseizing on the mandrel. The hollow body can now also be drawn to suchextent, on the same mandrel,

that the limit of elongation of the metal is attained. The severaldegrees of draught can also be substantially increased, as compared withthe known processes, since the material elongates more readily inconsequence of being loosened on the mandrel. For example, in thelmreindescribed process, copper-tube billets prepared in the Mannesmannmill and having a thickness of 6 mm. of metal and any convenientinternal diameter, such as mm., can be drawn to tubes with a thicknessof 1 mm. of metal, in 7 passes, without intermediate annealing andchange of mandrel. In the case of other metals and alloys, such as ironand ferro-alloys, similar conditions exist.

The invention has the further advantage that the work of inserting themandrel in the tube, and its withdrawal therefrom, has only to beperformed once, or at least more rarely than in the known processes. .Atthe same time, the risk of damaging the smooth surface of the tube isreduced. Moreover,

considerable saving in time is effected, since the intervals forchanging the mandrel are e:1tirelyor at least partiallydispensed with,and the wear on the mandrels is substantially reduced. I

In rolling tubes on a mandrel, it is known to employ, alternately withthe actual rolling apparatus, other rolling-means which loosen the tubeon the mandrel. This process, however, is suitable only for theproduction of tube billets of thick metal and inaccurate dimensions byhot rolling. In comparison with this known process, the inventionpresents the advantage that tubes, or similar hollow bodies, of anythickness of metal, even the however, is especially advantageous whenperformed in the following manner In order to prevent the movemenat ofthe work with the mandrel, and therefore avoid the risk of injury to themandrel by the movements, and also to.shorten the working periodconsiderabl the operation is per-- formed by fixing t e hollow body andmandrel in the drawing machinefor example,

the chain draw benchand drawing the die over the same by means of a toolcarriage travelling to and fro.

Loosening can be'efiected, after each pass or a few passes, by knownmeans, such as rotary reeling or hammering machines, which preferablymove in conjunction with the tool carriage and revolve round themandrel. They come into operation during the forward or return travel ofthe tool carriage, or simultaneously with the drawing operation. Incarrying out the invention, the mandrel may also be rotatably mounted,so that the loosening devices effect the rotation of the mandrel bymeans of their loosening movements, or the mandrel may be rotated byspecial actuating means. Greater advantage, however, is presented by'the new loosening process, which is distinguished by the use of verysimple devices which, being small, are easily disposed in the drawingmachine, and by particular reliability in operation and protectivetreatment of the work material and 'the surface of the work. This newloosening process is performed by working the hollow body on the mandrelon only a portion of its periphery, in such a way that any substantialelongation of the hollow body is avoided and that the flow set up in thematerial by the treatment takes a direction substantially tangential tothe axis of the hollow body. It has been found that the elasticity ofthehollow body loosens the unworked portion from the mandrel during theworking treatment, and loosens it all round afterwards, to an extentsufficient to allow a further drawing operation to be performed, or forthe hollow body to be stripped from the mandrel. Particularly elasticconditions are produced when the treatment performed with tools set atan angle causing a powerful flow of the material. In this manner,stresses which loosen the structural cohesion of the material at theparts subjected to work are avoided, and the orientation imparted to thecrystallites by the drawing operation is substantially unaltered. Theangle of setting means the angle formed by the axis of the hollow bodywith the tan gent at which the longitudinal-profile curve of the tool isapplied at the foremost point of contact (in the operative direction)between the tool and the material.

The ratio between the worked and unworked portions of the cross sectionwill vary according to the material and the thickness of metal of thehollow body, but must always be such that the total strength of theunworked portion of the cross section is greater than the resistance todeformation set up by the working of the worked portion, in order thatno substantial elongation of the hollow body ma be produced by theloosening treatment. ince, in the loosening operation according to theinvention, the material of the hollow body is deformed by toolsoperating in the direction of its length, and therefore in the samedirection as that-in which it flows when being drawn, and sinceexcessive stresses are revented by the flow permeating the thic ess ofthe material, this method of loosening is naturally far more favourableto the material properties of the hollow body than the known methods,because, in the latter, the flow pressure producing the loosening effectis applied at a larger or smaller angle to the direction of flow of thedrawn hollow body, which, in the case. of oblique rolls, amounts toabout 90. In such case, and particularly when the loosening is severaltimes repeated, the same loss of quality occurs as-is observed whenapiece of work, which has been deformed in one direcconfined to thesurface of the hollow body,

whereby powerful injurious stresses are set up in the material and, insome cases, lead to the hollow body tearing after stripping or duringfurther drawing. Hence, the invention has the additional advantage ofpreventing the waste hitherto resulting from the loosening treatment.

The new loosening process is performed, with particular advantage bymeans of tools which slide over the work, in the same manner as the die,since such tools can be set with the greatestaccurac and at a smallangle, and finally because, y reason of their small dimensions, suchtools can be very easily accommodated in any machine.

For example, loosening discs-with elliptical bore can be employed, whichset up a deforming action on only a small portion of the periphery ofthe hollow body, by means of the narrower parts of the bore. Suchloosening dies are drawn over the hollow body, 7

by the tool carriage, in the same way as the ordinary dies. They may bebrought into action when the machine is running idly, or inorder toreduce the working time, concurrently with the die. also be designed insuch a way as to possess adjustable working jaws, which can be set, byfine adjustment means, so as to produce the degree of. looseningrequired in such case. A particularly advantageous practice is toconstruct the tool which carries the jaws in sections and fit them inthat condition into the tool carriage.

The stripping of the hollow body from the mandrel can be effected bymeans of the known devices, but, in carrying out the invention, it ispreferable to employ a divided disc or bush having a bore of the same,or approximately the same diameter as the mandrel. This divided disc ismounted on the rear end of the mandrel and-after opening the front clampof the mandrelpushed over the mandrel by the retreating tool carriage,so that the hollow body is ejected from the machine in one operationwith the drawing and loosening operation, and with the mandrel always inthe same position in the machine. As compared, for exam 1e, with theundivided stripper this divide pattern offers the advantage that it canbe mounted in any convenient position on the mandrel without having toloosen the clamps of the mandrel and slide away the drawing tools whichhave already been drawn over the work. The divided stripper according tothe invention is preferably designed as a door, gate and the like,suitably connected with and moved by the tool carriage and, being set inThese new tools can ward, return or stop motion.

the open position during the drawing operation, assures free passage tothe die.

The invention can be carried out with advantage by means of existingtypes of drawing machines, such as chain drawbenches, drawing presses orthe like, the die being, for example, in a fixed position and themandrel, with the hollow body disposed thereon, drawn or pushed throughthe die. Still greater advantages, however, are obtained in respect oftime saving, simplicity of management, accuracy of work and the like incarrying out the invention by means of the drawing machine hereinafterdescribed with reference to the accompanying drawings in which Fig. 1shows, by Way of example, a diagrammatic plan of a tube-drawing machineconstructed and operating in accordance with the invention;

Fig. 2 is the corresponding side elevation of the machine shown in Fig.1;

Figs. 3 and 4 represent another embodiment in the same way.

Figs. 5 to 13 represent technical details of these machines.

In the embodiment shown in Figs. 1 and 2, the bedof ordinary pattern-ofthe drawbench carries, between guide rails 17, a tool carriage 8,designed as a tool rest and adapted to be moved to and fro by therotation of two or more threaded spindles 9. On the bench head is adivided clamping device 4 (which will hereinafter be described), whichis adapted to be opened and closed, and serves to grip the end' of thepiece which is to be worked. Power is transmitted to the spindles 9,which actuate the tool carriage 8, from a clutch 10which may beelectrically reversiblethrough pinions 11. The travel of the toolcarriage from forward to return movement is preferably reversed by meansof a switch 12, disposed at the head of the bench and serving to set theclutch for for- The cool carriage 8 contains a locking device 13 whichlooks the die 3 when closed, but, on being opened, leaves a sufiicientfree space, for the die to be drawn out of the carriage and replaced, ifdesired, by another die, loosening tool or the like.

The piece 2 to be treated is gripped, by means of its end, in the clamp4, after the dies have been threaded on said end, and the dies 3 arethen drawn, singly or in groups, over the work by means of thereciprocating tool carriage 8.

If the machine according to the invention is used for drawing hollowbodies over a mandrel, the mandrel 1with the hollow body (such as thetube 2) to be treated thereon, and the dies, (and, if necessary,loosening tools) 3is gripped at. the end by the clamp 4. The other endof the mandrel is gripped by a similar clamping device 6, connected witha freely movable cross head 5 in the machine, the movement of said crosshead being limited, in the direction of drawing, by suitable devices,such as stops 7, in order that the mandrel may remain stationary whilethe tube is being stripped oif. The stripper 14, which is preferablyconnected to the tool carriage 8, is opened during the drawing operationand leaves a free passage for the die, but is adapted to be closed, forthe purpose of stripping the tube, when drawing is terminated. If theloosening is not effected by means of elliptical loosening tools-whichare threaded, alternately with the dies, on the one end of the mandrelbefore commencing to draw-the loosening device 16 may be preferablyattached to the tool carriage. 15 is an auxiliary mandrel, which isadapted to swing on the pivot 15' and to slide in' the axial directionof the mandrel, and on which the dies and loosening tools can bethreaded, after the ejection of the tube, in order to facilitatethreading a fresh tube on the mandrel.

The method of operating is, for example, as follows v The forwardlytapered tube blank 2 is passed through the opened clamp 4 and-telescopedon the mandrel until the tapered tip of thetube bears against the stop1a formed by turning down the tip of the mandrel. The dies 3, which arearranged in proper succession on the swinging holder 15 are threaded onto the tip of the mandrel. The clamp 4 is then closed, and the machineis ready for drawing. On operating the electric switch 12, which setsthe known electric double-disc clutch 10 for forward or reverse running,as desired, by simple reversal, the tool carriage 8 is caused to advanceand return by means of the actuating mechanism 11 and the spindles 9,and the drawing operation proceeds in that, by means of the lockingdevice 13 on the tool carriage, one or more dies (for example 2) areengaged, each time, and drawn over the tube. Since the movable crosshead 5, which guides the mandrel accurately at the rear and by means ofthe clamp 6, and is fixed-by means of the stops 7only in the directionof the head end of the bench, slight changes in the length of themandrel, due to bending or to the elastic elongation resulting from thedrawing operation, can be balanced by slight movements of the cross head5 away from the stops 7 and towards the driving end of the machine. Thislongitudinal balancing can, of course, also be effected in any otherconvenient way, for example by sliding the mandrel in the clamp 6.

That loosening of the tube from the mandrel, which is necessary for thedrawing process, is efi'ectedaccording to the inventi0nfor example bysetting the loosening device 16 to suit the desired degree of loosening,and drawing it over the tube. This loosening is performed in a separateworking operation, during the forward or return travel of the toolcarriage, or in the same operat on as the drawing stroke. When theloosening has been effected, the loosening device is opened, to allowfree passage to the oncoming dies and enable them to be inserted in thetool carriage.

If loosening tools with elliptical bores be employed in place of theloosening device 16 travelling to and fro with the tool carria e, saidtools are threaded, together with the d1es in proper succession, on thetip of the mandrel, and, like the dies, are drawn over the tube b meansof the tool carriage. By suitably esigning the tool carriage, theloosening tool can be drawn over the tube after, and in the sameoperation with, the die, which it follows immediately or with a smallintervening space, so that no s ecial loosening stroke of the machine isnee ed and a saving of time is effected.

The reciprocating tool carriage is also rovided with a known lubricatingdevice Fnot shown), which moistens the work with lubricant after themanner of a drip lubricator. The lubrication is preferably combined witha circulating device, in which the lubricant escaping into the drawbenchis led into a co] lector and pumped back into the lubricator. Thetime-wasting lubrication by hand is done away with and betterlubrication is obtained.

In order to strip the drawn tube from the mandrel the clamp 4 is opened,the divided stripper 14 is closed and the tubewhich, is previouslyloosened from the mandrelis ejected through the opened clamp 4 by thereturn stroke of the tool carriage. The dies, which have been assembled,near the clamp 6, on the rear end of the mandrel, after the drawingoperation, are slipped over the mandrel back into position at the headend of the latter, after the devices on the tool carrier have been setso as to allow the dies a free passage. The dies can then be threaded,in exactly the same order and without any trouble, through the openingin the clamp 4 and on to the holder 16, which has been swung intoposition and reaches to the end of the man-- drel. The severaloperations are thenrepeated in the manner hereinbefore described. 7

Instead of being secured on the tool carriage, the loosening andstripping devices of the invention may, of course, be disposed in themachine in such a manner that they can be independently actuatedby thespindles 9. If loosening is necessary, for the purpose of stripping,after the termination of the drawing process, and if special stress islaid on surface quality and accurate gauge of the 3 tube, the lattermust be trued up after being stripped from the mandrel. In carrying outthe invention, however, this finishing process can also be performed inthe machine itself, prior to stripping, by employing, after the mandrelwithout difiiculty.

Figs. 5, 6 and 7 show, in elevation and Elan, a particularly suitableembodiment o the reciprocating tool carriage 8 of Fig. 1. This carriage,which is designed after the manner of a slide rest, is provided with twobores housing the two spindle nuts 19 and 20 by means of which the toolcarriage is moved to and fro by the rotation of the driving spind1es. Inorder to prevent the relatively long driving spindles from bending underthe weight of the carriage, the latter travels, like a slide rest, onledges 21 and 22, which are screwed onto the bed of the bench andprovide accurate guidance to the tool carriage. The carriage is providedwith a central opening 23 of such width that the tools employed, such asthe die (or loosening tool) 3 can pass through it without trouble. Themandrel clamps are disposed, both in the vertical and lateraldirections, in such a way that the mandrel 1 lies, unsupported, in thecentre of said opening 23. In the middle of the tool carriage is thelocking device, in the form of a gate 13, adapted to be raised by meansof a lever 25. This gate is provided, on the under side, with adownwardly opening gap 26, the width of which is onl a little largerthan the external diameter 0 the tube 2 carried on the mandrel. For thedrawing operation, this gateas is shown in the Fig. 7is raised by meansof the lever 25 far enou h to leave the opening 23 perfectly free, theie or loosening tool 3 being pushed through the opening and the gatelowered again. During the forward travel of the tool carriage, the die 3bears against the wall of the lowered gate and is drawn over the tube.

Figs. 8 and 9 show, in elevation and plan, a particularly suitable formof construction of divided stripper in accordance with the invention. 27is a frame having an opening 28 of the same width as the passage in thetool carriage, so that the die can be passed through it unhindered. Thisframe 27 is provided with four projecting lugs 29, between which, twodoor leaves 31 and 32 are adapted to swing on pivots 30. Said doorleaves are provided with gaps 33 in which can be insertedinterchangeable dividedbushes 34 having a bore equal to the diameter ofthe mandrel for the time being When the leaves 31 and 32 are closed(Fig; 8) the bushes enclose the mandrel with a sufiicient tightness foreffecting the stripping of the hollow body, and slide the tube off thefixed mandrel during the travel of the tool carriage. The opening andclosing of the two leaves 31 and 32 simultaneously-is effected by meansof two interengaging toothed quadleaves are closed, whereas, during thewhole of the drawing operation, they are kept in the open position asshown in Fig. 8, so as not to hinder said operation. This dividedstripper may, of course, also be designed in any other convenientmanner, for example in such way that the two halves can be caused toconverge and diverge by means of sliding keys or screw spindles.

Figs. 10 and 11 show, in elevation and plan, a particularly suitableform of the mandrel clamp 4 of Fig. 1. Two sliding members 41 and 42 areslidably mounted and accurately guided in two guide ledges 39 and 40.These sliders are provided with gaps 43 and 44 housing the half bushes45 and 46. On the sliders being pushed together, the head of the mandrelis firmly ipped by the bush, as indicated by the otted lines in Fig- 10.For stripping, inserting'and removing the dies, &c., on the other hand,the sliders occupy the position shown, so as to leave a sufficientpassage open between them and the ledges 39 and 40. The synchronousdisplacement of the sliders is effected by means of two threadedspindles 47 and 48 which are displaced in the axial direction by therotation of the threaded bushes 49 and 50, each of which is actuated,through a pair of pinions 51, 52

and 53, 54, from a common shaft .55, which is mounted in the crossframes56 and 57 supporting the guide ledges, and are caused to close andopen, as desired, by turning the hand wheel 58 to right or left.

Fig. 12 shows the manner in which the loosening action is effectedaccordingtothe invention. 59 is a loosening tool provided with anelliptical bore, and 1 is the mandrel carrying the tube 2 which is to beloosened. The tube 2 is now engaged and worked by the die solely at 60and 61, in the narrow part of the elliptical bore'in thatas is shown onan exaggerated scale in the drawingthe thickness of the tube wall isreduced by .a certain percentage at this place. The cross section of theelliptical bore is so calculated thatthe unworked portion of the tube,indicated by 62 and 63 in the drawing, prevents any longitudinalelongation of the tube, so that the material displaced at the points 60and 61 merely widens the tube, thereby increasing its diameter andproducing the desired looseningefi'ect. A loosening tool of this kind isneeded for each loosening within the series of the drawing passesprescribed in accordance with the invention. Thus ,if the treatmentcomprises 5 drawing passes and 5 loosenings,

5 dies and 5 loosenin tools accordin to Fig. 12 are employed, an aredisposed a ternate- 1y on the mandrel in corresponding gradation.

Particular advantages attaches to the employment of the twoart looseningtool ac cording to Fig. 13. n this tool, the elliptical loosening bores,such as 64, 65, 66, 67 are machined in such a way that the separatingjoint lies along the major diameter of the ellipse, Where no deformingaction takes place. This tool is preferably mounted in the tool holderand is vertically and laterally adjustable, for example by means ofwedges, in sucha Way that ,when open, it allowsthedie to pass betweenits operative surfaces, whilst, when closed, it allows the desiredloosening bore to be brought into operation. If this divided looseningtool be provided with another bore 68 adapted to the diameter of themandrel, the same tool can also be emplo ed for stripping the tube offthe mandrel, t us rendering a separate stripping tool superfluous.

A divided tool with only a single 0 ening may also be employed forloosening. n such case, the operative surfaces of said 0 ening must becapable of adjustment to each esired degree of loosening, for whichpurpose knownmeans can be used. This arrangement dispenses with theexpensive elliptical bores, and therefore corresponds to a considerablereduction in cost. This divided loosening tool can also be suitablyattached to the reciproeating tool carriage 8 of Fig. 1, and isconstructed in such a way as to allow unrestricted performance of thedrawing operation when open, Whereas, when closed, the operativesurfaces are brought into contact with the tube, for the purpose ofloosening it. For example, use can be made with advantage, of anarrangement shown in Figs. 8 and 9 the onlymodification being that, inplace of the divided bush 34, irons with elliptical or straight drawingsurfaces are attached on the leaves 31 and 32, and that the pivots 30are mounted in eccentric bushes which enable the operative surfaces tobe correspondingly converged. During the drawing operatlon, the leaves31 and 32 are opened into the position shown in Fig. 9. Before theloosening operation they are closed, that is, moved into the positionshown in Fig. 8, and are then set to the requisite loosening gauge bymeans of the said eccentrics. Of course, the operative surfaces of thesaid loosening device can be for example, is drawn over the tube d (dcordance with the invention, several mandrels, instead of a single one,are arranged in the machine and drawing is effected simultaneously onthese mandrels, the several parts being designed accordingly. In this"way, the return stroke of the tool carriage also can be utilized forthe actual operation of drawing. Fig. 4 shows in plan, a suitableembodiment of a machine for such a process. a denotes the frame of themachine; 0, c 0 c are the mandrels over which the tubes are drawn; (1',d", d and d are the tubes which are to be drawn; f, f f 7'" are thedevices for locking the dies, which are adapted to be actuated by meansof the tool carriage f and the spindles b and b g'-g" are rows of dies,which are passed, in succession or 1n grou s, over each tube. The tipsof the man rels 0 and c are clamped in the fixed crosshead l at k andis, their other ends being clamped, at m and m in a movable crosshead l.The mandrels c and 0 are secured in a similar manner in the movablecrossheads n and 0. These last two are driven by the gearing e throughthe spindles p and 12 In the first working operation, a die 9 and (g)for example, is drawn over the tube d (d) and, after reversingthemachine, a die 9 (9 It is known that the work undergoes considerableelongation at each drawing pass. In order to prevent this elongationcausing the machine to run idle,the procedure adopted according to theinvention consists in imparting a corresponding relative displacement tothe two clamps, WhlCll clip the work in a machine, during or at the endof each drawing pass. Accordingly, for example, during the forwardstroke of the machine, the crossheads in which the two mandrels c and care gripped are moved backwards, by means of the gear mechanism 6, tothe same'extent as the tubes have stretched in the first pass. Thereciprocating tool carriage now, by means of the diesheld by the lockingdevices, alternately draws the tubes d and 01 during the forward stroke,and the tubes d and d during the return stroke, until the final dieshave operated and the tubes are ejected in a finished condition.

The loosening operations needed for the purpose of drawing andstripping, and the stripping operation itself, are effected in themanner previously described. I g

This process has the great advantage that, without any increase in theworking staff, the output *of drawn tubes can be increased, in one andthe same machine, and in a-p roximately the same time, two to fourfol(according to the number of mandrels) as compared with the output of asingle-mandrel machine. This naturally implies a considerable reductionin the cost of production.

The hereindescribed process may obviously be applied to the productionof other hollow blank by a drawing operation, loosening the blank fromthe mandrel, and repeating said drawing and loosening operations whilesaid hollow body is continuously retained upon said mandrel, and atleast, one end of said body being maintained in its original position onthe mandrel.

2. The invention as set forth in claim 1, wherein two sets of hollowbodies are simultaneously formed, and the drawing operation fordecreasing the diameter of one set of the hollow body blanks is effectedsimultaneously with the loosening of the second set of blanks, and theloosening of the first set of blanks is effected simultaneously with thedrawing op erations performed upon the second set.

3. The process of manufacturing hollow bodies which comprises the stepsof supporting the hollow body blank on a mandrel, drawing down the blankby repeated passes through drawing dies, and loosening the blank fromthe mandrel after each of a plurality of said drawing passes, said blankbeing retained substantially in its original position on said mandrelthroughout the entire process.

4. The invention set forth in claim 3, wherein said loosening isefiected by progressively applying at successive transverse sectionsalon said body blank pressureexerted radially o the blank and atcircumferentially spaced portions of the periphery thereof.

5. In the formation of. seamless pipe from a short thick-walled blank bya series of passes through drawing dies, the process which compriseslacin securing one end t ereo to an elongated stationary mandrel,successively moving a series of drawing dies over the entire length ofsaid blank to reduce the external diameter of and to elongate the same,loosenin the blank from said mandrel between two 0 said drawingoperations, and stripping the blank from said mandrel only at thecompletion of the drawing operation.

6. The process as set forth in claim 5,

the blank on and wherein a loosing operation follows each drawingoperation.

7. The method of forming hollow bodies which comprises, positioning ablank upon a mandrel, subjecting said blank while substantially in itsoriginal position on said mandrel to a series of drawing operations toreduce the diameter of the blank, subjecting said blank to suchloosening, intermediate the first and last drawing operations, that thecreep of the blank on the mandrel during the drawing operations issufiicient to prevent the occurrence of tension cracks in the blankduring drawing, and stripping said finished body from said mandrelsubsequent to the last drawing operation.

In testimony whereof I aflix my signature HERMANN VON FORSTER.

